This invention relates generally to internal combustion engines and more particularly to a poppet valve which will remain closed against pressure differences acting on opposite sides of the valve.
Conventional double cylinder engine concepts are limited by problems associated with the expander inlet valve. These problems are typically, 1) continuous high pressure in the inlet passage increasing valve stem leakage, 2) high pressure differences across the valve acting in opposite directions, against which the valve must remain closed, and 3) very short valve event, requiring high valve operating speed.
Injection of the fuel could take place either upstream of the expander inlet valves, or in the expander cylinders, or both. However, the injection and valve timing would be arranged such that the pressure rise due to combustion would occur almost entirely in the expander cylinders. Therefore, the expander inlet valve must use an unconventional arrangement because it must be capable of staying closed while there are substantial pressure differences acting across the valve in opposite directions
Valve operating speed is a key constraint when trying to operate at high piston speed. In order to achieve high enough power density to compete with the conventional reciprocating internal combustion engine, in an engine employing reciprocating compressors and expanders, it is necessary to achieve similar high piston speed. At a volume ratio of 10, the inlet valve event length for an expander is combustion engine. The inertia loads in a reciprocating valve system are inversely proportional to the square of the length of the valve event. Therefore the inlet valve train in the expander will experience inertia loads 16 times greater than those in an engine of the same size, valve area, and piston speed. The effect will be relieved somewhat at lower volume compression ratios, but is still a major constraint.
A conventional pressure balance scheme includes a balance piston which increases the area and decreases the length of the leakage path past the valve stem which aggravates problem 2 mentioned above. Also, the balance piston increases the reciprocating mass of the valve which aggravates problem 3 mentioned above. Further, the balance piston may be more difficult to lubricate than a valve stem.
The foregoing illustrates limitations known to exist in present devices. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.